The Genomic Instability Core will be housed in the UCLA Clinical and Molecular Cytogenetics Labs located in a 3000 sq ft space in the Rehab Building on the UCLA campus with considerable facilities for providing standard cytogenetics and Fluorescence In Situ Hybridization (FISH) services for investigators working on both Human and Mouse cells. Chromosomal aberrations are sensitive indicators of a previous exposure to ionizing irradiation. The Core's objectives are to provide cytogenetic services to project and pilot research program investigators in the UCLA-CMCR. For Projects 1 and 3, the aims are: 1) to determine the effect of radiomodulatory compounds on chromosome aberrations in cells from mouse embryos (Project 1), and 2) to characterize the effects of the same compounds on radiation-induced chromosomal aberrations in human cells, including cells from patients with radiosensitive/repair deficiency syndromes (Project 3). The Core will use various cytogenetic and molecular cytogenetic techniques to achieve these aims, including karyotyping, chromosome/chromatid breakage studies, and micronuclei analyses. The studies will be supplemented by FISH experiments with centromere-specific probes for numerical abnormalities such aneuploidy, region specific probes for structural aberrations, telomere-specific probes for chromosomal integrity studies, and whole chromosome paints and 24-color multicolor FISH for complex chromosome aberration analyses.